Step 4: The scale

Step 5: This is about how it looks when you're riding.

It's on the third-smallest cog here.

I really don't like to cross-chain. It's never been a problem before, since I've always had a pretty good sense of what rear cog I'm in. But when I got a bike with a compact double after riding 12 years with a triple, it seems like I'm shifting the front so often that now it's hard to keep track of things. So I made a shift indicator using scrap plastic that's kind of inconspicuous, and you don't need to remove the cable to install it.

Warning - if you get frustrated fiddling around with small things until they're just right, don't even start this project. And, I'm the only one who ever handles my bike, so the fact that it's a bit fragile isn't a problem for me.

Step 1: What you'll need

No, not the toothbrush - the toothbrush package (or whatever other small piece of clear plastic you can find). I used the toothbrush package because the right-angle bend was already formed permanently into it.

And a bit of duct tape, which I forgot to put in the picture.

Step 2: The pointer

Shift into the biggest cog and pick a spot on the cable where you'll be able to see the pointer when you look down. It's going to move away from the fork as you change gears. You need something that will attach securely enough to the cable, and be visible enough to see through the window. A piece of duct tape works well. Cut it about 1/4" wide and 1-1/2" long and wrap it tightly around the cable. Tweezers are helpful.

Step 3: The window

Cut the window from the toothbrush package. The window needs to be about 1-1/2" long, and wide enough to go out from the frame about 1/8" past the cable. Stick it onto the down tube with double stick tape, referring to the pointer to position it.

If your question is - Does adjusting the rear derailleur affect the reading you get from my indicator - the answer is No. The indicator actually shows you which position of the shift lever you are indexed into. Adjusting the rear derailleur just brings the position of the cage and small pulleys into the correct alignment with whatever cog you are currently in, but doesn't affect what the indicator is showing you.

Thanks for your answer. Yes, that is my question. When you say " Adjusting the rear derailleur just brings the position of the cage and small pulleys into the correct alignment with whatever cog you are currently in" I interpret that it means that looking at the gauge, you may think that you are using a speed when are actually using another. Is that so?

No, that's not going to be a problem. The gauge doesn't actually show anything about the derailleur - it only tells you what position the shift lever is in. The only way you could have a problem is if you made such a huge adjustment of the derailleur that when your shift lever was indexed to the third position, the derailleur was actually in the fourth cog (we would really have to call that a mis-adjustment). But the gauge would still show that your shift lever is in the third position, just like it is supposed to show. (When I talked about "the position of the cage and small pulleys", I hope it was clear that I was talking about the cage that holds the pulleys on the rear derailleur and not my indicator gauge.)

My problem with my old style Shimano 18 speeds shifter is that I never know what rear gear I am using. The setting is very unstable, it depends on so many parameters that often the chain goes more o less than I want. Pardon my poor English.

Idea to maybe make this even easier, you could use a hanging file folder plastic tab - some of the hanging file folder tabs have almost like a little rounded bead at the top where the cable would slide beautifully. They also come in different colours so you could match your bike. Here's a link to a sample of the type I'm talking about http://www.kmart.com/office-impressions-hanging-file-folder-plastic-index-tabs/p-025V043854071000P

This is a great idea. I just bought my first road bike, so I'm a little disoriented without a gear indicator, and this is something I could actually do without messing with the bike at all or any special tools. Great job!